A TrCH encoder of a base station encodes a PCH or a DL-SCH to transfer it to a modulator. The modulator performs transmission using a PDSCH on two channels from among a plurality of downlink transport channels.
In reference to “3GPP TR 25.814 v7.1.0—Version September, 2006” for the implementation of an LTE-Advanced system, a resource allocation scheme between the PDSCH and other physical channels is not clearly defined.
Accordingly, a node B scheduler allocating a resource to the PDSCH allocates the resource to the PDSCH as a localized type or a distributed type. If other transmitted physical channels are allocated to the allocated resource, the PDSCH uses an overwrite type through an occupied physical channel.
Based on such a method, for the PCH or the DL-SCH transferred by the TrCH encoder, a method (where the modulator calculates beforehand how many bits are transmitted by codeword per PDSCH before performing modulation by TTI unit and enables safe transmission of the bits through the channel) is satisfied by multiplying a resource block (which is allocated by codeword per PDSCH) by an Orthogonal Frequency Division Multiplexing (OFDM) symbol which is transmitted during 1 TTI.
In this way, the number of bits to transmit is easily obtained, but if a control channel occupies a resource to which the PCSCH is allocated, loss of a PDSCH signal is inevitable.
In LTE standard “3GPP TS 36.211 v8.4.0—Version August, 2008”, which is one of the standards that are referred to as the basis for the development of a current LTE-Advanced system, a resource allocation scheme between the PDSCH and other transmitted physical channels has been clearly defined.
For the PCH or the DL-SCH transferred by the TrCH encoder of the base station, calculation (on how many bits the modulator transmits by codeword per the PDSCH by TTI unit) is necessarily performed in an L1 controller or the node B scheduler that is the upper layer of the modulator, and thus, the PCH or the DL-SCH is not only used in the upper layer but is also transferred to the TrCH encoder and the modulator. Accordingly, downlink transmission is smoothly performed.
However, while a Cell-Specific Reference Signal (CSRS), Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS) and Physical Broadcast Channel (PBCH) are allocated to a region to which a resource for the PDSCH is allocated, or PDSCH resource allocation is performed as the localized type or the distributed type due to factors such as a precoding type, because the number of layers, a modulation type, a transmitted antenna set and the number of codewords transmitted to a user terminal, the number of the bits of the PCH or DL-SCH which is actually transmitted by transmitted OFDM symbol varies.
Accordingly, for the PCH or the DL-SCH transferred by the TrCH encoder, the modulator has difficulty in calculating in advance how many bits it transmits by codeword per PDSCH before performing modulation by TTI unit, and it is difficult to check the number of transmission bits beforehand in the L1 controller or the node B scheduler that is the upper layer of the modulator.